Preach it, teach it, model it.
For the youth, address it in forums (with older youth/parents/teachers as panel) and at annual camps as a seminar/workshop topic... let it come from their peers and people they look up to like sports heroes. Modelling it is effective. Speak to leadership and get them to join the pastors as effective family models for the congregation. Where there are breaches in sexual conduct address them quickly. Teach the positive -- show them what good and healthy relationships are. Have a premarital course for those who are dating. Address issues openly but confidentially in a small group context (group counselling, perhaps).
